Andrea's Marbles

It is given that she lost 1/4 th ,that is 5 of them .Therefore she has 15 of them left.

$Andrea\quad has\quad 20\quad marbles.\quad She\quad loses\quad \frac { 1 }{ 4 } \quad mean\quad she\quad loses\quad 5\\ Remainig\quad marbles=20-5\\ \\ \boxed { Remainig\quad marbles=15 }$

Answet is $20 × \left(1 - \dfrac{1}{4}\right)\\ = 20 × \dfrac{3}{4}\\ = \color{#69047E}{\boxed{15}}$

If Andrea loses $\frac{1}{4}$ , she is left with $1- \frac{1}{4} = \frac{3}{4}$ which is $\frac{3}{4} \times 20 = 3 \times 5= \boxed{15}$ marbles

20/4 = 5 i.e. she lost 5 marbles then 20-5= 15

If Andrea loses $\frac{1}{4}$ of her marbles, she would have:

1 - $\frac{1}{4}$ = $\frac{3}{4}$ marbles.

Now she has $\frac{3}{4}$ marbles of her initial 20, which is

$20*\frac{3}{4}$

= $\boxed{15}$

1/4th of 20 = 20/4 = 5 and it is written that she loses 1/4th of the marbles, so she is left with 20-5=15 marbles and that is the correct answer!!!!!!!